Someone buying a used bitsa for £200 can't expect too much, but OTOH they could get a used Squier for similar.
If the seller enthuses that they've put a lot into the build, set it up, and so-on, then perhaps the buyer could take them at their word.
It's possible that the buyer got GAS and then someone else looked at it and went "hang-on, it's got issues".
Given that you mention "customer satisfaction", it is possible that the buyer took you to be a business and is therefore viewing it as a fault with a retail purchase.
They might've become disillusioned with the whole thing.
I'd be wary of buying Chinese parts and tarting them up, as their quality can be questionable - I've had a couple of howlers.
Mostly "yebbuts" from my side, but I do hope it gets sorted satisfactorily for both sides!